#!/bin/sh
#
# Copyright 2014 Google Inc. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

: ${XSECURELOCK_XSCREENSAVER_PATH:=@path_to_xscreensaver@}

TAB='	'

# Note: the following logic is somewhat derived from parse_screenhack in
# XScreenSaver.
convert_xscreensaver_programs() {
  i=0
  while IFS= read -r line; do
    skipwhite() {
      while :; do
        case "$line" in
          $TAB*) line=${line#$TAB} ;;
          \ *)   line=${line# } ;;
          *)     break ;;
        esac
      done
    }
    skipwhite
    # Read disabled field.
    case "$line" in
      -*) enabled=false; line=${line#-}; skipwhite ;;
      *)  enabled=true ;;
    esac
    # Strip visual name (VISUAL:, where VISUAL can't contain " or whitespace).
    case "${line%%[\" $TAB]*}" in
      *:*) line=${line#*:}; skipwhite ;;
    esac
    # Strip textual description ("description").
    case "$line" in
      '"'*) line=${line#\"*\"}; skipwhite ;;
    esac
    # What's remaining is the program name with its options.
    echo "$i $enabled $line"
    i=$((i+1))
  done
}

convert_program_list() {
  i=0
  while IFS= read -r line; do
    echo "$i true $line -root"
    i=$((i+1))
  done
}

list_savers() {
  want_all=$1
  if [ -f ~/.xscreensaver ]; then
    printf "%b" "$(
      xrdb -n ~/.xscreensaver 2>/dev/null |\
      grep ^programs: |\
      cut -d : -f 2-
    )" | convert_xscreensaver_programs
  else
    ls "$XSECURELOCK_XSCREENSAVER_PATH" | convert_program_list
  fi | while read -r number enabled saver flags; do
    $want_all || $enabled || continue
    [ -x "$XSECURELOCK_XSCREENSAVER_PATH/$saver" ] || continue
    printf '%d\t%s/%s\n' "$number" "$XSECURELOCK_XSCREENSAVER_PATH" "$saver $flags"
  done
}

mode=

# Debug mode to list all savers.
case "$1" in
  --list_savers)
    list_savers false
    exit 0
    ;;
  --list_all_savers)
    list_savers true
    exit 0
    ;;
  --internal-override-mode=*)
    mode=${1#*=}
    ;;
esac

if [ -z "$mode" ]; then
  mode=$(
    xrdb -n ~/.xscreensaver 2>/dev/null |\
      grep ^mode: |\
      cut -f 2
  )
fi

selected=
case "$mode" in
  one)
    selected=$(
      xrdb -n ~/.xscreensaver 2>/dev/null |\
        grep ^selected: |\
        cut -f 2
    )
    ;;
  random)  # NOT random-same.
    # Try bash's $RANDOM, but if it's not there, just use the PID.
    selected=${RANDOM:-$$}
    ;;
esac

if [ -z "$selected" ]; then  # Note: random-same hits this.
  # We're using the parent process ID here, which may be a saver_multiplex
  # instance. This ensures that multiple instances of this always spawn the same
  # saver on each screen.
  selected=$PPID
fi

# Prepare the saver list so we only parse once.
case "$mode" in
  one)
    savers=$(list_savers true)
    count=$(printf '%s\n' "$savers" | wc -l)
    ;;
  *)
    savers=$(list_savers false)
    count=$(printf '%s\n' "$savers" | wc -l)
    ;;
esac

select_saver() {
  case "$mode" in
    one)
      printf '%s\n' "$savers" | grep "^$selected$(printf '\t')"
      ;;
    *)
      printf '%s\n' "$savers" | tail -n +$((selected % count + 1))
      ;;
  esac | head -n 1 | cut -f 2-
}

# On SIGUSR1, we exit the saver and retry the selection.
sigusr1_caught=false
trap 'sigusr1_caught=true' USR1

while :; do
  saver=$(select_saver)
  if [ -z "$saver" ]; then
    echo >&2 "xsecurelock: No saver selected. Giving up."
    exec ./saver_blank
  fi
  sigusr1_caught=false
  eval $saver
  status=$?
  if [ $status -eq 0 ] || $sigusr1_caught; then
    # Immediately try the next saver.
    case "$mode" in
      one)
        ;;
      *)
        selected=$((selected + 1))
        ;;
    esac
  else
    # Saver failed entirely. Just give up.
    echo >&2 "xsecurelock: Screen saver failed with status $status: $saver."
    sleep 2  # Anti-spam delay.
    if [ x"$mode" != x"random" ]; then
      # As a fallback, when the saver failed, try random.
      exec "$0" --internal-override-mode=random
    fi
    exit $status
  fi
done
